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I have a sp 4 port 13b, stock intake manifold, and a carter (edelbrock) 400cfm carb. I could never get the car to idle decent, always kinda loped and rocked. Figured I'd switch to direct fire to see if that'd help, so i ordered some ignitors and planned on doing that in the next couple of weeks.
In the meantime, I bought a rebuilt 625 cfm carter and a holley blue top. When I went to put the new carb onto the stock manifold, I realized the previous owner shortened the throttle shaftes so he could put the carb on. I'm not industious enough to try doing that, so I was gonna buy a used RB holley intake or jay-tech intake off ebay. But I'm not only lazy, I'm also cheap. So instead I ordered 2 2" (needed 4" of rise) aluminum carb spacers to use with the stock intake manifold to see how it'd work. I got them today and put them on in about 90 minutes since I had to fabricate some fasteners. I decided to first use the original 400 cfm carb that was on there to see if I noticed any difference. So i just unbolted the carb, slid the new 4" spacer under it, and bolted it back up.
How did they work? In one work AMAZING. It smoothed the idle out so much it's ridiculous. There's also no bucking when driving at low rpms and when driving a constant speed it's incredibly smoother. The difference is truly night and day.
Power? The butt-o-meter is telling me low rpm is a little better in the 2-3k range. Lost some grunt under 2k though. 3k-7k, it seems to pull much stonger. All in all I'm very, very pleased with the outcome. Total cost was $40 for the two spacers + ~ $5 at menards on threaded rod and nuts.
Next step is to put the larger 625 carter on and get the blue top installed.
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You can get carb spacers from any hotrod shop. I happened to order mine from here: http://expressauto.zoovy.com/product/S2066B because they were cheap and close to me. Quality of the part was nothing great, but they could've been cleaned up with a little work.
I used the open design spacer. I had wanted to go with the 4 hole, figuring the torque and power would benefit more. But I was impatient and ordered the open design ones.
The idea behind using carb spacers is similar to using an intake with longer runners. I'm sure I benefited greatly since I was using the very short stock intake manifold, when I should have had something like the RB intake to go with the 4-barrel carb.
This winter I still plan on buying a proper intake, this was merely a stop-gap measure so I can keep driving the car until I have the cash for the intake. It was also an interesting experiment. I'm curious to see what other spacer heights would do, and how the 4 hole vs. open design would be. But I doubt I'll look into it a whole lot more.
I had a spacer below the Holley also, only took it out because I replaced it with a nitrous spray plate
I wonder if that is why Weber side draft carbs work so well on rotary engines, the runners are almost twice as long as on a Holley since they sort of wrap around. The longer intake runners move the powerband up in the rev range, and we all know rotaries like to rev!!
those hi-rise spacer plates with the center wide open, not the 4 hole jobs. for me in the past on my shelby and on my buddys small block ford V8 do work very well.
in my duel plane intake and my buddys single plane intake.. the mid-range on the single plane engine with solid lift and 4 speed was much greater then my duel plane solid lift 4 speed. for a couple of years now i've wondered how would an open hi-rise spacer work on a 12a with stock nikki and intake. just like the intakes that wrap around for a weber or other side drafts, distance seems to work in a rotory engine too. are you saying you 'stacked' spacers ?
yes, I took 2 of the 2" open spacers (not the 4 hole) and bolted them together, effectively making one large 4" spacer. This created a large chamber in-between the carb and intake manifold. It probably results in a loss of intake velocity, but creates a better place to get good air/fuel mixing. I ended up making my own "bolts" out of 5/16" threaded stock to hold the two spacers together, with a gasket in between. Seemed to work decent and I was able to snug up everything pretty good.
But in looking at pictures, it seems that the 4" rise is about the same as what the jay-tech intake was like and I'm assuming it's very close to the RB version. I also knew I'd have clearance issues ( i was running a 6" tall K&N filter ) so I bought one of the edelbrock low profile triangle shaped filters. $20 at Pepboys, only downfall is that it doesn't seem to flow as easily as my K&N was.
I can take some pics tonight and post them if there's any interest.
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